It is desirable to provide full collision protection for robots on the same rail at high-speed motion, with speeds as high as 3000 mm/sec along a rail direction, and small carriage separation distance, as close as 70 mm, with no additional hardware.
Previously, a method for collision avoidance for all of the robots along a rail included a controlled stop event, requiring all of the robots connected to different controllers to have the same deceleration rate. Problems emerged with this system when some robots performed an emergency stop due to an unanticipated servo error event that caused immediate servo-shut off while the remaining robots were subject to a controlled stop. This caused collisions to occur between the trailing robots and the leading robots where the controlled stop controller moved the corresponding robots to a commanded position using the programmed deceleration rate, while the emergency stop shut off the servo and resulted in a short deceleration distance for the remaining robots.
To have full protection, if one robot on the rail performs an emergency stop due to any servo error condition, then ideally the remaining robots on the same rail have to use the same emergency stop as soon as possible to avoid any collisions.
Prior systems use PLC, Ethernet Link Control and PMC/IO Link or any combination of hardware and software solutions. However, none of these solutions can provide the needed performance that can effectively protect against collision. A PLC control takes too long to detect the servo error condition from one controller and then take the proper action to stop the robots in different controllers. Additional hardwire connections from the PLC to each controller are also required.
The disadvantage of an Ethernet Control Link is that the non-deterministic transmission delay time across the controller can result in a collision. The disadvantage of a PMC/IO Link is the cost and delay. This type of link is too costly to make the hardware connections among all the controllers. Further, the delay time is large where the Master PC resides on one controller only.
U.S. Pat. No. 5,347,459 discloses a method for detecting a collision between a robot and one or more obstacles before it occurs. Generally, a plurality of voxels defines a finite work space and each grid element is assigned a value representing the relative strength and distance of the robotic manipulator to an object and subsequent collision potential. The robot is modeled by spheres in a voxelized workspace. Each voxel within the workspace is assigned a value which corresponds to its distance from the closest obstacle. A collision is determined to be imminent if the voxel value at the center of a sphere is less than the radius of the sphere in voxels.
U.S. Pat. No. 6,282,460 discloses a method for preventing collisions between robots using a central controller to communicate with each robot. Each robot is programmed to automatically stop when the robot reaches a certain point in the operation.
The central controller causes a first robot to stop or pause so that a second robot may safely complete an operation. The central controller allows the robots to resume operations when it has been determined that the robots have reached their respective correct positions. The method includes using a pendant controller to provide stop commands to a robot as instructed by an operator.
U.S. Pat. No. 6,493,607 discloses a collision checking system which can be performed in order to determine if a collision will likely result by simulating movement of the robot in accordance with a general motion plan developed from the motion of a robot within a free space confined by obstacles. The collision checking system provides a pre-determined collision-free path of at least one fixed robot within a confined work area.
U.S. Pat. No. 6,678,582 discloses a method of avoiding collisions between robots based on continuous predicted configurations and forecasted stopping distances. The method allows for automatic configuration of the work space from a collision avoidance standpoint. It determines automatically which components have potential collisions with which other components by predicting the configurations of the moving components over a period of time sufficient enough to allow the machines to stop safely and check for interference. If a collision is predicted, the machines are commanded to stop on or off their paths.
U.S. Pat. App. Publication No. 20060129348 discloses a system for collision avoidance of rotary atomizers by measuring both the drive-side motion quantities of the drive system, and the driven side quantities, i.e., on the driven mechanism. The dynamic model contemplates the inertia of various components of the system, the elastic components, and the frictional forces or moments of the drive system and the mechanism, respectively. For disturbance-free operation of the drive system, the two comparison values must agree, while a deviation between the two comparison values can indicate a disturbance or even a collision. A monitoring device is provided for each shaft of the robot to recognize any deviation of the actual behavior of the drive system from the modeled behavior.
U.S. Pat. App. Publication No. 20060182536 discloses a Cartesian robot cluster tool architecture that includes at least two robots for performing a task within a confined workspace. A collision avoidance system includes a system controller that monitors the position of each of the robots by use of various sensors positioned on the robot(s) or in the cluster tool during the transferring process to avoid a collision. The system controller is adapted to actively alter the motion and/or trajectory of each of the robots during the transferring process to avoid a collision and minimize the transfer path length. Preferably, the disclosure provides a cluster tool configuration so that if one of the robots becomes inoperable the system can still continue using the other robots. This configuration also removes, or minimizes, the need for collision avoidance type control features since the physical overlap of robots that are positioned next to each other is eliminated.